Plant Reproductive Structures Research Articles

Interrelationships between Acremonium lolii, Peramine, and Lolitrem B in Perennial Ryegrass

Perennial ryegrass (Lolium perenne L.) is commonly infected with the endophytic fungus Acremonium lolii in a mutualistic relationship. The fungus produces a number of alkaloids, some of which are responsible for causing livestock disorders and/or for conferring insect resistance to the host grass. Little is known about the interrelationship between fungal growth and alkaloid production in the ryegrass plant and how this varies throughout the year. The concentrations of A. lolii and two of its alkaloid metabolites, lolitrem B and peramine, were monitored in basal (mainly leaf sheath) and upper (mainly leaf blade) parts of 17 endophyte-infected ryegrass plants on a monthly basis for 1 year. A. lolii, lolitrem B, and peramine concentrations were lowest in winter. The highest A. lolii concentrations were recorded in early summer, which coincided with the development of plant reproductive structures. Lolitrem B concentrations were highest from summer to early autumn and were consistently highest in the basal part of the plant. Peramine concentrations were generally highest in the upper part of the plant. Individual plants contained different levels of A. lolii, lolitrem B and peramine. These differences were generally maintained throughout the year. Although data for each month were variable, regression analyses showed that yearly mean concentrations of lolitrem B and peramine in individual plants were closely related to, and therefore probably largely determined by, yearly mean concentrations of A. lolii.

Cultural impacts on macrophytes in the Yahara lakes since the late 1800s

Vegetation changes in the Yahara lakes around Madison, Wisconsin, USA, are evaluated using historical data. Present vegetation is less diverse and less extensive, produces less biomass and is composed of more disturbance tolerant species than it was 80–100 years ago. Many changes are related to human impacts that began about 150 years ago which directly altered plant habitat, decreased water clarity, were toxic to plants, removed plant biomass or reproductive structures, or resulted from exotic invaders. The impacts are interrelated and overlap in time and space so change did not occur from simple cause and effect relationships. However, cumulative effects of the impacts are very evident. Management recommendations are made that are applicable to North American lakes with a similar history.

Girdle and Plant Part Associations of Threecornered Alfalfa Hopper Nymphs (Homoptera: Membracidae) on Soybean

Plant part and girdle associations of Spissistilus festinus (Say) instars on soybean, Glycine max (L.) Merrill, were investigated by inspecting randomly selected whole plants. Locations of many nymphs changed from stem to nonstem stmctures as plant development increased and later back to stem structures as lateral branches became available. Third to fifth instars preceded first and second instars in these changes. A large proportion (≥39%)of nymphs was associated with main stems regardless of plant phenology. Association of nymphs with plant reproductive structures was least (2%) during blooming and greatest (13%)during pod fill. Association of nymphs with stem and petiole girdles increased with nymphal age. Also, a greater proportion of older nymphs was oriented above girdles. Girdle association was higher for nymphs on leaves and petioles than for those on stems, but most nymphs were not associated with girdles. The absence of differences in associations of S. festinus instars with reproductive structures contrasted with the differences observed in associations with girdles, suggesting that the factors responsible for nymphal association with the two types of structures may differ.

MOLECULAR ANALYSIS OF HEAT STRESS PROTEINS IN HIGHER PLANTS

When plants experience high temperature stress, they respond by synthesizing a discrete set of proteins called heat shock proteins (HSPs). This response is not unique to plants, but is observed in all other eukaryotes. It is now known that the HSPs are evolutionarily conserved proteins, and furthermore, that HSPs function not only during stress, but also during normal growth and development. My laboratory has characterized several of the major groups of HSPs in higher plants. We have cloned genes encoding plant HSP70 proteins and low molecular weight (LMW) HSPs (17-23 kDa). Using this information we have investigated the expression of HSPs both in the field, and under laboratory conditions which mimic field situations. We have determined the temperature limits for expression of HSPs in vegetative tissues, and have also found that HSPs are frequently produced in plant reproductive structures, even in the absence of stress. As a first step toward understanding HSP function, we have characterized the intracellular localization of HSPs. Results show that there are unique HSPs in the cytoplasm, chloroplast and endomembrane system. These ubiquitous proteins appear to play essential roles in many cellular processes.

Contrasting Vegetation Responses Following Two Forest Fires in Northeastern Minnesota

Abstract: Response of Pinus banksiana Lamb, forest communities during the first growing season following a spring fire (three communities) was contrasted with response following a summer fire (two communities) in northeastern Minnesota. Differences in both quantity and quality of vegetation were related to degree of destruction of the forest floor. The spring fire destroyed the litter layer, but left much of the cool, moist lower layers intact, protecting the plant reproductive structures within them. The summer fire consumed virtually all of the warmer, drier forest floor and most of the associated reproductive structures. Reproduction following the spring fire developed vegetatively and prolifically, while that following the summer fire developed primarily from seed and was less abundant. The summer fire also liberated more nutrients from